The present invention relates to a method for removing catalyst residues from olefin polymerization products.
The insufficient removal of catalysts, and in particular, their halogen components, from liquid olefin polymer results in many undesirable problems. For instance, the presence of catalyst residues may cause the discoloration of the resulting polymerization products, the generation of hydrogen halide gas due to the thermal degradation of the catalyst, the degradation or decomposition of the organic compounds due to structural change during subsequent distillation, the poisoning by halogen contaminants of the hydrogenation catalyst during subsequent polymer treatment by halogens which are contained in the polymer as a contaminant, etc. It is therefore desirable to remove the catalyst residues from the polymerization product as fully as possible before the subsequent treatment and/or use of said products.
U.S. Pat. No. 4,476,297 discloses a process for removing catalyst residues from polyolefins prepared with catalysts containing light metal halides and titanium and aluminum compounds. This process comprises suspending the polyolefin in a liquid medium and treating the mixture with an aliphatic monocarboxylic acid and then separating and washing the recovered polyolefin.
U.S. Pat. No. 4,547,620 relates to a process for removing the halogen component from a halogen-containing organic compound produced from a halogen-containing catalyst selected from the group consisting of Friedel-Crafts catalyst and Ziegler catalysts. The process comprises contacting the halogen-containing organic compound with a hydrotalcite compound.
U.S. Pat. No. 4,122,126 discloses a method for removing an aluminum halide or its complex catalyst from a polymerization product prepared by employing said catalyst. The method comprises mixing the polymerization product with an aprotic polar solvent at a temperature of 70.degree. to 150.degree. C. and then filtering the mixture within the same temperature range.
U.S. Pat. No. 3,904,498 relates to a process for removing catalytic residues from reaction products which comprises admixing an aqueous solution of an alkali or alkaline earth metal hydroxide with the reaction product to precipitate the catalyst residues as hydroxides or salts and separating precipitated catalyst residues from the resultant mixture.
U.S. Pat. No. 3,992,432 discloses a process for catalyzing heterogeneous ionic organic reactions in a system of multiple liquid phases. Catalysis is effected by introducing into the system a quaternary ammonium salt.
U.S. Pat. No. 4,028,485 discloses a process for removing hydrogenation catalyst residue from solutions of hydrogenated olefins or olefinic polymers which comprises treating such solutions with non-aqueous acid followed by neutralization with an anhydrous base and filtration.
Thus, the prior art discloses various methods for the removal of catalytic residues from polymerization products. However, since the catalyst residues or their complex compounds are present in the polymerization products in a state near dissolution, it is very difficult to remove catalyst residues completely from the polymerization products with the conventional physical methods.
Other common prior art methods employed for removing halogen-containing catalyst components from olefin polymerization products involve washing with water and/or an aqueous alkaline solution. When water is employed to wash the olefin product, the yield of organic compounds recovered is reduced. This is due mainly to the difficulty encountered when separating the organic compound layer from the water layer. This separation can be accomplished only with poor efficiency. Furthermore, this procedure is labor intensive and requires large and complex facilities for treating the separated water layer. Several difficulties are also encountered when an aqueous alkaline solution is employed for removing catalyst residues. Initially, separation of the oil layer from the aqueous layer can be accomplished with only marginal efficiency resulting in reduced yields of organic product. Additionally, the alkali leads to the formation of a colloidal hydroxide precipitate which requires an additional facility to remove the by-product precipitate. Finally, both washing methods require a significant amount of time. Most current commercial processes employ five aqueous caustic/water washes. Each wash step is followed by as much as 16 hours of settling to effect good oil/water separation.
Accordingly, it is an object of the present invention to provide a process for the removal of catalyst residues from liquid olefin polymerization products.
Another object of this invention is to provide a process for removing catalyst residues from reaction products prepared with Friedel-Crafts type catalysts and other Lewis acids or Ziegler-type catalysts.
A further object of this invention is to provide a method for removing catalyst residues from liquid olefin polymerization products which minimizes the time and process steps required to separate such residues from the reaction product.
Another object of this invention is to provide a process for purifying liquid olefin polymerization products from discoloring residues.
Upon further study of the specification and appended claims, further objects and advantages will become apparent to those skilled in the art.